Sven, I wouldn't take down the recips at all -
1. Some LL's do take months, literally months, to list you. 2 weeks is definitely too short a time (some of the big ones with the most traffic take 3-4 weeks).
2. Why waste time tracking down who listed each site and then waste more time replacing recips? Just build another FS instead
What I do is this. Once a month or so, I take a close look at my stats. If a LL I have been submitting to for a few weeks sent zero traffic, I stop submitting to it. I don't take the recip off any old sites, but I don't add it to any new sites and I quit submitting to those LL's and try new ones instead.